Morphology and composition of Au catalysts on Ge(111) obtained by thermal dewetting

Abstract

International audienceWe investigate the chemical and morphological structure of the Au nanodots on Ge(111) which serve as catalysts for the formation of epitaxial Ge nanowires. The spatial localization of Au is investigated by X-ray spectromicroscopy and transmission electron microscopy. We show that dewetting of an Au film on Ge(111) gives rise to a thin Au-Ge wetting layer and Au-Ge dots. These dots are crystallized but not with a single crystallographic orientation. Thanks to the spatially resolved X-ray and transmission electron microscopy measurements, a chemical characterization of both binary Au-Ge catalysts and wetting layer is obtained at the nanoscale. We show that Ge vertical growth is achieved even without external Ge supply

A review of wetting versus adsorption, complexions, and related phenomena: the rosetta stone of wetting

“…Examples include catalysis [101][102][103], porous electrodes [104,105], and more recently charge storage for memory applications [106][107][108].…”

Eutectic Combinations as a Pathway to the Formation of Substrate‐Based Au‐Ge Heterodimers and Hollowed Au Nanocrescents with Tunable Optical Properties

“…In situ TEM has, in fact, been used to monitor the sideways nucleation of both Si and Ge from supersaturated liquid alloys resting on either SiO x or SiN x membranes. Similar structures formed on (111) Ge substrates are, however, observed to exhibit up‐down directionality . Together, these results suggest that substrate influences could provide an avenue for asserting control over the segregation direction.…”

“…The Au‐Ge combination is ideal for heterodimer fabrication due to their near‐complete immiscibility in the solid state, a binary phase diagram with a deep eutectic ( T E = 361 °C) and a sizeable Ge vapor pressure below its melting point ( T m = 938 °C) . The assembly process begins with the formation of substrate‐immobilized Au nanostructures able to act as heterogeneous nucleation sites for Ge adatoms.…”

“…While much emphasis has been placed on nanowire growth, recent interest in Au‐Ge and Ag‐Ge heterodimers has occurred both from the standpoint of garnering a mechanistic understanding of the early stages of nanowire growth and from devising synthetic pathways yielding nanostructures with unique properties due to a coupled response. Notable studies include: (i) the in situ TEM monitoring of Au‐Ge heterodimer formation via various growth modes, (ii) the manipulation of catalyst composition as a means to promote fast VLS nanowire extrusion rates, (iii) the colloidal formation of Au‐Ge and Ag‐Ge heterodimers, (iv) silica‐embedded Au‐Ge nanostructures exhibiting reversible phase change behavior when sequentially exposed to ultraviolet light and heat, (v) the formation of bi‐lobed Au‐Ge nanostructures on [100]‐oriented Si and (vi) the modification of [111]‐oriented Ge surfaces by Au nanostructures which, upon temperature cycling, consume and then precipitate Ge . Nanostructures of greater intricacy have also been derived from the segregation of Au and Ge from a liquid AuGe alloy confined within a HfO 2 encasement and through the use of a co‐sparking technique .…”

Dynamics of thermally induced assembly of Au nanoislands from a thin Au layer on Ge(001)

“…Annealing above the eutectic temperature resulted, in turn, in the formation of randomly oriented, droplet-like, crystalline nanoislands supported on the Ge pedestals. [22][23][24] In this paper we report on Scanning and Please do not adjust margins Please do not adjust margins helps in the formation of the Ge nanorods. 19 Crystalline Au nanoislands half-buried in the substrate are observed on the samples cooled down to Room Temperature (RT) after annealing to temperatures above the bulk eutectic temperature.…”